Metallic gaskets are commonly utilized at the joint between members to be joined, for example, cylinder heads and cylinder blocks which constitute pars of internal combustion engines. Such a metallic gasket has beads which are formed to seal the deck surfaces of the cylinder head and the cylinder block, and the beads form elastic seal lines on the deck surfaces owing to the tightening forces of tightening means such as tightening bolts for uniting the members to be joined, to provide a sealing effect.
In recent years, reduction in weight, improvement in performance, and improvement in economy have been desired in the field of internal combustion engines, and there have been demands for the development of internal combustion engines having increased durability. Since internal combustion engines are commonly used over a long period of time, they are frequently exposed to thermal deformation, expansion, contraction or the like. Therefore, metallic gaskets which can withstand thermal deformation due to the internal combustion engines have been desired as metallic gaskets for sealing the joints between cylinder heads and cylinder blocks. For these reasons, Applicant developed the gasket of copending U.S. Ser. No. 07/114,699, U.S. Pat. No. 4,799,695, which gasket is an attempt to improve durability. The gasket of this application has an intermediate plate and a compensation plate which are superimposed to constitute an intermediate constituent member, with a peripheral edge portion of the compensation plate adjacent to a combustion chamber hole being bent to form a compensation portion, and base plates each having a bead respectively disposed adjacent the surface of the intermediate plate and the surface of the compensation plate.
When a cylinder head is fastened to the cylinder block by tightening bolts with a metallic gasket interposed therebetween, the cylinder head is curved by the bolt tightening force and, in particular, the space between the cylinder head and the cylinder block around the combustion chamber increases. As a result, distortion may occur.
In such a metallic gasket, the peripheral edge portion of the compensation plate that is adjacent to the combustion chamber hole is only bent toward the intermediate plate so as to form the compensation portion. Therefore, the function of the compensation portion, that is, its stopper function, does not sufficiently work upon the bead of the base plate which is disposed on the side on which the peripheral edge portion of the compensation plate that is adjacent to the combustion chamber hole. For this reason, when in use, the beads may undergo knocking by the influence of explosive force or the heat of an internal combustion engine, with the result that their spring characteristics may deteriorate to cause lowering in the sealing properties and durability.
Also, in such a metallic gasket, the beads formed on the two superimposed base plates have the same bead height. Accordingly, the bead of the base plate disposed on the side on which the peripheral edge portion of the compensation plate which constitutes a portion of the intermediate constituent member, that is, the bent peripheral portion which is not located adjacent to the combustion chamber hole is depressed to an excessive extent. As a result, the spring forces of the base plates non-uniformly act upon the bead portions, so that uniform sealing pressure cannot be obtained at each of the deck surfaces. Therefore, sealing properties deteriorate, and the beads of the base plates are permanently set due to their fatigue resulting from excessive depression. This may incur a deterioration in durability.
It is therefore an object of the present invention to provide a laminated metallic gasket in which a compensation bent portion is formed in an intermediate constituent member so that a first step formed between one surface of a bent peripheral edge portion of the intermediate constituent member that is adjacent to the combustion chamber hole and one surface of the intermediate constituent member is made approximately equal to a second step formed between the other surface of the bent peripheral edge portion of the intermediate constituent member that is adjacent to the combustion chamber hole and the other surface of the intermediate constituent member, whereby the compensation portion can provide a sufficient compensation effect upon the beads of the respective base plates which are laminated on the intermediate constituent member so as to protect the beads, thereby preventing a lowering in spring characteristics of the beads and enhancing sealing properties as well as durability.
It is also an object of the present invention to provide a laminated metallic gasket in which the bead height of the bead of a base plate disposed on the side on which is located the peripheral edge portion of an intermediate constituent member which is bent to form a compensation portion adjacent to a combustion chamber hole is larger by a predetermined amount than the bead height of the bead of a base plate located on the other side of the intermediate constituent member, whereby the spacing between deck surfaces created around the combustion chamber is compensated for and a deterioration in the function of the beads is prevented and whereby the spring force of each of the base plates at the bead portion is made uniform to improve sealing properties and durability and, in addition, it is possible to easily alter the spring characteristics of the base plates.
To achieve this object, in accordance with the present invention, there is provided a laminated metallic gasket provided with two base plates each made from an elastic metal plate on which a bead is formed such as to surround a combustion chamber hole, an intermediate constituent member being interposed between the two base plates, characterized in that the beads of the respective base plates are disposed symmetrically with respect to the intermediate constituent member, a peripheral edge portion of the intermediate constituent member that is adjacent to the combustion chamber hole being bent to form a compensation portion having a predetermined thickness, and a compensation bent portion being formed in the intermediate constituent member so that a first step formed between one surface of the bent peripheral edge portion of the intermediate constituent member that is adjacent to the combustion chamber hole and one surface of the intermediate constituent member is made approximately equal to a second step formed between the other surface of the bent peripheral edge portion of the intermediate constituent member that is adjacent to the combustion chamber hole and the other surface of the intermediate constituent member.
To also achieve this object, the present invention provides a laminated metallic gasket provided with two base plates each made from an elastic metal plate on which a bead is formed such as to surround a combustion chamber hole, an intermediate constituent member being interposed between the two base plates, characterized in that a peripheral edge portion of the intermediate constituent member that is adjacent to the combustion chamber hole is bent and radially overlapped relative to the peripheral edge portions of the two base plates that are adjacent to the combustion chamber hole to form a compensation portion having a predetermined thickness, the bead height of a bead of one of the base plates disposed on the side on which is located the peripheral edge portion of the intermediate constituent member which is bent to form the compensation portion adjacent to the combustion chamber hole being larger by a predetermined amount than the bead height of a bead of the other located on the other side of the intermediate constituent member.
In the arrangement of the present invention, for the purpose of compensation for the clearance which is created around the combustion chamber between the deck surfaces of the cylinder head and the cylinder block, the peripheral edge portion of the intermediate constituent member that is adjacent to the combustion chamber hole is bent to form the compensation portion which is thicker than the bead portion in the vicinity of the combustion chamber hole. In addition, the first step formed between one surface of the bent peripheral edge portion of the intermediate constituent member that is adjacent to the combustion chamber hole and one surface of the intermediate constituent member is approximately equal to the second step formed between the other surface of the bent peripheral edge portion of the intermediate constituent member that is adjacent to the combustion chamber hole and the other surface of the intermediate constituent member. Accordingly, the beads of the respective base plates which are laminated on the intermediate constituent member can be protected by the compensation portion, so that a deterioration in their spring characteristics is inhibited to enhance sealing properties and durability.
In accordance with the arrangement of the present invention, when the laminated metallic gasket inserted into a joint undergoes deformation due to compression, the bead of the base plate disposed on the side on which is located the peripheral edge portion of the intermediate constituent member which is bent to form the compensation portion adjacent to the combustion chamber hole is prevented from being deformed due to compression by virtue of the peripheral edge portion of the intermediate constituent member that is adjacent to the combustion chamber hole. Since the amount of deformation of a smaller bead of the base plate disposed on the other side of the intermediate constituent member is small, the spring force of each of the base plates at the bead portions is made uniform to uniformly seal the entire sealing surfaces, thereby improving sealing properties and durability. In addition, a deterioration in the function of the bead of each of the base plates can be prevented to improved durability.